Organizing pneumonia (OP) is a rarely diagnosed disease, however the incidence ratio was estimated as 6-7/100000. Disease can occur in cryptogenic form or as a secondary reaction to various noxious agents, drugs, and ionising radiation, as a concomitant disease to infections, lympho- and myeloproliferative disorders, and connective tissue diseases. Symptoms of OP are non-specific therefore lung biopsy and histological examination are necessary for diagnosis. Eighteen cases of OP, 15 women and 3 men, aged 40 to 76 years, are presented with analysis of clinicopathological characteristic and therapeutic problems. In all cases diagnosis was confirmed by open lung biopsy. In one case radiotherapy and in one trastuzumab treatment was the cause of OP. In further 3 women antibodies against Chlamydia pneumoniae and in one--against Mycoplasma pneumoniae were found in serum. Probably Hashimoto disease was the cause of one case. In 12 patients the OP was idiopathic. Majority of patients were treated by prednisone (0.5 mg/kg). In one patient regression without any treatment was noticed and in other one--after cessation of trastuzumab. Five women were treated by clarithromycin. In 3 of them regression was observed but in other 2 corticotherapy was necessary. The observation period ranged from 1 month to 9 years, mean 34 months.